Pain is a frequent and disabling consequence of metastatic prostate cancer in humans. The cause of this pain is unknown, but is likely to involve mediator-dependent signaling by tumor cells to spinal nerve roots. A candidate mediator, the potent vasoconstrictive peptide endothelin-1 (ET-1), is secreted in high concentrations by metastatic prostate cancer cells and is known to induce pain in animals and in humans. This proposal seeks as its broad long-term objective to establish the molecular basis of spinal nerve root pain due to metastatic prostate cancer. Preliminary studies demonstrate that ET-1 applied to rat sciatic nerve produces pain behavior that is 1) ETA receptor-dependent, and 2) likely due to direct actions on sensory afferents. The goals of the proposed studies are to combine results from in vivo neurophysiology and in vitro cellular physiology in order to establish: Specific Aim 1: The selectivity of ET-1's actions or excitation of functionally-identified peripheral axons Specific Aim 2: the ionic and cellular mechanisms by which ET-1 produces neural excitation Specific Aim 3: The importance of ionic and cellular targets, identified in vitro, for ET-1 induced pain behavior in vivo The findings from these experiments will thus define a role for ET-1 in the pain produced by metastatic prostate cancer, identify which sensory afferents mediate ET-1 induced pain, and analyze the ionic and cellular mechanisms that underlie ET-1's excitatory effects on sensory neurons. This information should help to identify: 1) new and useful directions for research into the mechanisms underlying pain produced by metastatic prostate cancer, and 2) novel targets for drug development aimed at treating this pain.